The technique of hydraulic fracturing (commonly referred to as “fracing” or “fracking”) is used to increase or restore the rate at which fluids, such as oil or gas, can be produced from a reservoir or formation, including unconventional reservoirs such as shale rock or coal beds. Fracing is a process that results in the creation of fractures in rocks. The most important industrial use of fracing is to increase the rate and ultimate recovery of oil and natural gas by stimulating oil and gas wells; usually the fracturing is done from a wellbore drilled into reservoir rock formations.
Hydraulic fractures may be created or extended by internal fluid pressure which opens the fracture and causes it to extend through the rock.
Hydraulic fractures may be created or extended by internal fluid pressure which opens the fracture and causes it to extend through the rock. Fluid-driven fractures are formed at depth in a borehole and can extend into targeted formations. The fracture height or width is typically maintained after the injection by introducing an additive or a proppant along with the injected fluid into the formation. The fracturing fluid has two major functions, to open and extend the fracture; and to transport the proppant along the length or height of the fracture.
In a multi stage well treatment, multiple zones within a well are created by deploying a treatment string using ports that can allow treatment fluid to flow from the treatment string into the formation. The treatment string can have a multitude of packers that can be set between each of the ports to create isolated zones, thus forming a barrier during each fracturing treatment. Each port is selectively opened by a ball, plug, or dart that is pumped from surface; the ball, plug or a dart lands onto a seat that is located inside each of the ports. By increasing the pressure behind the ball, plug, or dart, after it has landed on the seat, enough force can be created to shift the seat and open the port (allowing the pressure from inside the tubing to contact the formation). Each seat in the port can be sized to accept a ball of a certain diameter but at the same time allow balls of a smaller diameter to pass. A disadvantage to this system is that as different sized balls must be used for each portion; there is a practical limit to the number of portions that the bore can be divided into.
Current fracing systems and methods can be problematic and inefficient. For example, current ball drop systems suffer from the same restrictions on the size limitation of the internal diameter of the treatment string. In some cases, if the largest internal diameter of a ball that is allowed 3.750″, and assuming ⅛″ increments of change in ball diameter, a well will be limited to having an approximate maximum of twenty-four stages.
There have been attempts and developments to increase the number of zones in a well by introducing indexing mechanisms that have a multitude of inactive positions and one active position. These mechanisms use a ball or a dart to force the seat into different indexing positions. These mechanical counting mechanisms, however are complex have been used with limited success.
Further mechanical attempts to provide a mechanical counter are disclosed in Canadian Patent Nos. 2,844,342 and 2,794,331. These mechanisms rely on a ball or the force of the ball to shift a seat downstream in order to place a counter into the next position. Since the ball can land on the seat of the tool at a high velocity, the impact that is created has a potential of damaging the mechanism. In addition, these mechanisms provide no positive feedback via a pressure signature to surface (which is an important diagnostic function that provides feedback as to whether all of the tools are counting correctly). For example, as the ball passes through each tool at high velocity, the impact and pressure behind the ball would not stop the ball for long enough for a pressure increase to be detected at surface. Also, the mechanism (particularly the counting grooves) is fully exposed to debris during cementing and fracing operations, which could all cause the counter to jam, skip or fail. It is therefore desirable to provide more reliable tools and methods that do not rely on mechanical forces to move counters into their designed states. It is therefore also desirable to provide more reliable tools and methods that provide positive feedback regarding the counting function, and are protected from debris.
The methods and apparatuses currently available have their shortcomings. Accordingly, there is a need to provide a tool and method that overcome the disadvantages of the prior art. In addition, it is desirable to provide more reliable tools and methods that do not rely on the direct mechanical force of a ball against a seat to move a seat into different counting positions.